1. Field of the Invention
The present invention relates to a display device and a method for manufacturing the same, and more particularly, relates to an active matrix display device including pixel circuits for pixel electrode switching and to a method for manufacturing the above display device.
2. Description of the Related Art
In recent years, attempts to develop a display device, such as electronic paper, having flexible properties have been made. In the display device as described above, organic thin film transistors (TFTs) formable on a plastic substrate by a low-temperature process are each used as a switching element which drives a pixel electrode. In addition, in order to reduce cost, a printing process has been intensively introduced in manufacturing of the display device as described above.
In manufacturing of a display device which includes organic TFTs, when photolithography for resist pattern formation and reactive ion etching using a resist as a mask are used, as the case of a silicon TFT, to form connection holes in an interlayer insulating film, due to damage caused by a developer and/or a stripper used for a resist, and plasma damage during reactive ion etching, transistor properties are liable to be degraded. Hence, in manufacturing of a display device including organic TFTs, in order to form an interlayer insulating film having connection holes, it has also been desired to use a printing process.
In addition, the display device as described above, which uses organic TFTs as switching elements, is necessary to satisfy a resolution of 150 dots per inch (dpi) or more. In this case, the size of one pixel is reduced to 200 μm square or less. Hence, a connection hole which connects a pixel circuit including a switching element to a pixel electrode provided thereabove with an interlayer insulating film interposed therebetween is necessary to have an opening diameter of 50 μm or less.
However, when an interlayer insulating film including connection holes each having an opening diameter of approximately 100 μm is formed by screen printing, the number of mesh intersections supporting an emulsion pattern of a 500-mesh screen plate, which is generally used, is only several. Hence, through repeated printing, printing defects caused, for example, by peeling of emulsion portions may occur. Furthermore, an interlayer insulating film including connection holes having an opening diameter of approximately 50 μm may not be practically formed by screen printing.
Accordingly, a method has been proposed in which via posts are printed beforehand at connection portions of pixel circuits, and an interlayer insulating film is then printed by a screen printing method or an inkjet method, and a method for manufacturing a display device using the above method has also been proposed (see Japanese Unexamined Patent Application Publication No. 2006-295116, and “Journal of Applied Physics” 2004, Vol. 96, p. 2286).